Fan



March 7, 1950 E. E. HANS 2,500,071

FAN Filed March 12, 1948 2 Sheets-Sheet 1 W X 5 v 4a. 5'

INVEN TOR. Q OMZ/A/D 5/70/10 FTgZ.

March 7, 1950 E. E. HANS 2,500,071

FAN

Filed March 12, 1948 2 Sheets-Sheet 2 INVENTOR.

[DMZ/N0 f Haws Patented Mar. 7, 1950 UNITED STATES PATENT OFFICE FAN This invention relates to improvements in fans. In many types of heating and air conditioning systems for instance, such as those used in busses, a hollow casing is provided in which air is treated, and this treated air is discharged by a fan mounted in an orifice formed in the casing, in such an arrangement the casing intensifies the fan noise to such an extent that it becomes very annoying. a

The noise created by a fan, when in operation, consists of two separate sounds, air noise, which is a swishing sound caused by rapid flow of the air itself, plus pitch noise, which is usually a relatively high metallic ring caused by the flowing air coming in contact with the fan blades and the resultant vibration thereof.

I find that the intensity of the pitch noise at any given speed is dependent, among other things, upon the spacing of the blades, that is upon the number of blades employed for each inch of diameter of the fan. For instance, if a fan is pro-.

vided with five substantially fiat radial blades for eachinch of diameter (say 40 blades in an 8 inch fan)", or less, the pitch noise is clearly audible over the air noise; however, if the number of blades is increased to six for each inch of diameter (say 48 blades in an 8 inch fan) the pitch noise is drowned out by the air noise, and is no longer audible to the human ear. Again, with seven similar blades per inch of diameter (say 56 blades in an 8 inch fan) the pitch noise is still undetectable to the human ear.

I find that as the number of blades is increased from say three to six for each inch of diameter of the fan (that is from 24 to 48 in an 8 inch fan) the air output is reduced by something less than five percent (for instance from 350 to 335 cubic feet) but if the number of blades is increased to approximately seven per inch of diameter (say 56 blades in an 8 inch fan) the output drops sharply. For instance with 56 blades of identical size and form to those used in a 48 blade fan, which delivers 335 cubic feet of air, and rotating at the same speed, an 8 inch fan only delivers about 270 cubic feet. In other words. by gradually increas ing the number of substantially fiat blades to approximately six per inch of diameter of the fan a point is reached where the pitch noise drops in proportion to the air noise and is drowned out by the latter so that it can no longer be detected by the human ear. There is perceptible drop in the decibel rating of the fan when that po nt is reached, and, moreover, that point is reached prior to the inclusion of so many blades that the air output is materially lessened. This holds true a perceptible pitch noise when only a small num-v ber of blades are used per inch of diameter, and

in fans of all sizes it is practical to make with such a relatively large number of substantially fiat blades; the practical size range being from about four inches to about twelve inches in diameter.

It is an object of the invention to provide a fan so constructed and proportioned that the normal air noise drowns out the pitch noise, irrespective of speed of rotation, so that the pitch noise cannot be detected by the human ear.

Another object of the invention is to provide such a fan which is relatively cheap and simple to manufacture.

Having thus stated some of the objects and advantages of the invention, I will now describe it in detail with theaidof the accompanying drawings, in which: 1

Figure 1 shows a side elevation of my fan mounted in an orifice.

Figure 2 is a front view thereof.

Figure 3 shows one disc and the blades integral therewith.

Figure 4 is a section on the line 4-4 of Figure 2, showing the two discs and one blade extending from one of the discs.

Figure 5 is a view on the line 5--5 of Figure 1 showing the gap between two adjacent blades and portions of their discs.

Figure 6 is a section of a blade on one disc. taken as a section on the line 6-6 of Figure 3, and

Figure '7 is a corresponding section of a blade on the other disc.

Referring to the drawings, l designates an electric motor mounted in a split collar 2 having radial arms 3 the outer extremities of which are secured, as by screws 3a, to an orifice 4, which, in the present instance, is formed integral with a hollow casing 4a. This orifice is coaxial with the shaft 5 of the motor I. Secured on a hub 6 fixed around the shaft 5 is a fan 1 consisting of two superimposed discs 8 and to each having a like number of similarly shaped integral blades 9 and 9a respectively projecting therefrom. These blades rotate concentrically in, and project somewhat forwardly of the orifice l, the bore of which is only slightly larger than the diameter of the fan.

The discs 8 and 8a are relatively so positioned that each blade extending from one disc is centrally positioned between an adjacent pair of blades extending from the other disc; and all the blades are in alignment in a plane extending at right angles to the axis of the said discs. In order to accomplish this the blades integral with each disc project farther laterally from the inner sides of their discs than from the outer sides of the latter, since the common longitudinal center line of all the blades coincides with the contacting inner faces of the discs, as may be clearly seen in the drawings. Moreover the blades I and 9a, which are transversely inclined and are arranged in substantially overlapping relation throughout their length, extend substantially radially from the discs 8 and 8a, and are preferably fiat both longitudinally and transversely. In order to facilitate assembly of the discs and their blades, 9. slot III is formed in the leading edge of each blade 9 at its inner extremity, and formed in the trailing edge of each blade id at its inner extremity is a corresponding slot Illa.

I find that in order to reduce the pitch noise of the fan relative to the air noise so that the former is effectually drowned out by the latter and rendered inaudible to the human ear, it is necessary to restrict the distance between adjacent blades 9 and 9a at their outer peripheries. With only five blades for each inch of diameter of the fan (that is with a distance of substantially 3%" around the fan circumference between the center lines of adjacent blades at their outer peripheries), irrespective of what that diameter may be or the speed at which the fan is operated, pitch noise is clearly audible if the fan is rotated sufiiciently fast to produce air noise. But as the number of blades for each inch of diameter is increased from five to six a point is reached where the pitch noise drops proportionately to the air noise and becomes inaudible to the human ear; moreover, at that point there is a perceptible drop in the decibel rating. It may also be remarked that by increasing the proportionate blade number from five to six the air output is only reduced by approximately two percent; whereas if the number of blades is further increased to seven for each inch of diameter (that is a distance of substantially 5%" around the fan circumference between-the center lines of adjacent blades at their outer peripheries), the reduction in air output is approximately twenty percent. Consequently by increasing the number of blades per inch of diameter a point is reached where the pitch noise is inaudible, and this occurs just prior to the time that so many blades are included that they materially reduce the efficiency of the fan. The above figures hold equally true irrespective of the width of the blades, whether they are flat or slightly curved, and whether the blades actually overlap or are sufiiciently narrow that a slight gap occurs between adjacent blades from their outer peripheries when looked at in a direction parallel with the fan axis.

a What I claim is:

1. A fan including a hub, a plurality of u iformly spaced blades carried thereby, and said fan having more than five blades for each inch of diameter whereby, upon rotation of said fan, the air noise created renders the pitch noise inaudible to the human ear.

2. A fan including a hub, a plurality of uniformly spaced, substantially fiat blades carried thereby, the fan having more than five blades for each inch of diameter, whereby, upon rotation of said fan, the air noise created renders the pitch noise inaudible to the human ear, and said fan having less than seven blades for each inch of 4 diameter whereby the air output is not materially lessened by multiplicity of the blades.

3. A fan including a hub, a plurality of uniformly spaced blades carried thereby in substan- 5 tially overlapping relation, said blades being substantially fiat throughout their length and breadth and their outer peripheries being concentric throughout their length, and the proportionate number of blades per inch oi. diameter 10 of the fan being more than five whereby, upon rotation of the latter, the air noise created renders the pitch noise inaudible to the human ear.

4. A fan including a hub, a plurality of uniformly spaced blades carried thereby in substantially overlapping relation, said blades being substantially fiat and their outer peripheries being concentric throughout their length, and the proportionate number of blades per inch of diameter go of the fan being more than five and less than seven whereby, upon rotation of the fan, the air noise created renders the pitch noise inaudible to the human ear and at the same time the air output is not materially" lessened by multiplicity u of the blades.

5. A fan including a hub having two superimposed discs fixed thereon, uniformly spaced blades projecting radially from each disc, each blade projecting from one disc being spaced equidistant between two adjacent blades proiecting from the other disc, and the total number of blades projecting from the two discs being more than five for each inch of diameter of the fan whereby, upon rotation of the latter, the air noise 3 created renders the pitch noise inaudible to the human ear.

6. An arrangement including an orifice, a shaft mounted for rotation and extending coaxially through the orifice, a fan including a hub fixed Q on the shaft and radial blades carried by the hub,

the outer peripheries of the blades be ng in close proximity to said orifice and extending therein, said outer peripheries being concentric with the hub axis throughout their length, and the number 3 of blades being more than five for each inch of diameter of the fan, whereby, upon rotation of the latter, the air noise created renders the pitch .noise inaudible to the human ear.

'7. An arrangement including an orifice, a shaft I mounted for rotation and extending coaxially through the orifice, a fan including a hub fixed on the shaft and radial blades which are substantially flat carried by the hub, the outer peripheries of the blades being adapted to rotate u in close proximity to said orifice and partly within the latter, the number of blades being more than five for each inch of diameter of the fan, whereby, upon rotation of the latter, the air noise renders the pitch noise inaudible to the human so ear, and the number of blades being less than seven for each inch of diameter whereby the air output is not materially reduced by multiplicity of the blades.

8. A fan including a hub, a plurality of unias formly spaced, substantially fiat blades carried thereby, and the number of blades being such that the distance around the fan circumference iretween the center lines of adjacent blades at their outer peripheries is less than ii" whereby, upon 70 rotation of the fan, the air noise renders the pitch noise inaudible to the human ear.

9. A fan including a hub, a plurality of unii'ormly spaced blades carried thereby, said blades being in substantially overlapping relation, and

7 the number of blades being such that the distance around the fan circumference between the center lines of adjacent blades at their outer peripheries is less than ii" and more than 9;" whereby, upon rotation of the fan, the air noise renders the pitch noise inaudible to the human ear and yet the blades are not sufiiciently closely spaced to materially reduce the air output.

10. A fan including a hub having two superim posed discs fixed thereon, uniformly spaced blades projecting radialiy from each disc, each blade projecting from one disc being spaced equidistant between two adjacent blades projecting from the other disc, all the blades being in substantially overlapping relation, and the number of blades being such that the distance around the fan cir cumference between the center lines of adjacent lclades at their outer peripheries is less than it whereby, upon rotation of the fan, the air noise renders the pitch noise inaudible to the human can ill. An arrangement of the character described including a hollow casing having an orifice there-= in, a motor mounted with its shaft coaxial with the orifice, a fan including a hub having super imposed discs secured thereon, said hub being fixed on said shaft, each disc having integral radiating blades, the blades being uniformly spaced on each disc, each blade on one disc being equidistant between two adJacent blades on the other disc, said blades being positioned partly within and in close proximity to the orifice, and the total number of blades on the two discs being more than five for each inch of diameter of the fan whereby, when the latter rotates, the air noise created renders the pitch noise inaudible to the human ear.

REFERENCES CIITEHD The following references are of record in the iile of this patent:

UNITED STATES PATENTS Number Name Date 3,773,349 Bothezat Aug. 19, 193d 1,863,00t3 Garner July 19, 1932 2,328,072. Aug. 31, 1943 

